1. Field of the Invention
The present invention relates to an injection device for a low melting point metallic material capable of molding a metallic product by directly injection-filling a die with a molten low melting point non-ferrous metal.
2. Detailed Description of the Prior Art
A desired metallic product has been molded by melting a low melting point non-ferrous metal (for example, lead, zinc, tin, aluminum, magnesium or its alloy, etc.) in a heating cylinder with a plunger or a screw installed inside and measuring the molten metal as in the case of plastics, thereafter, injection-filling the die with the metal directly or via a hot runner from the nozzle of the heating cylinder tip by forwarding movement of the plunger or the screw, and cooling it, thus forming desired metal products.
In injection-molding of such metallic materials, unlike plastic materials, a completely molten liquid phase metallic material has little viscosity and hardly causes fluid resistance. Therefore, a measuring means adopted for a conventional in-line screw injection device causes a back-flow of the measuring material due to the injection load pressure by the forwarding movement of the injection screw and decreases the quantity, and this makes the measurement very unstable and makes it difficult to form metallic molded goods with favorable molding accuracy.
As a solution of this problem, the metallic material is not completely molten but the injection-molding is carried out in a semi-molten state by limiting the melting temperature at the solidus curve temperature or higher and at the liquidus curve temperature or lower. A texture of a molten metal in this temperature range is in a semi-molten state (thixotropic state), and this causes fluid resistance to some extent, and leakage of the measurement material due to back-flow caused by the injection load pressure is decreased in compared with that in the liquid phase. Therefore, the measurement is stabilized by excessively measuring a decreased volume by the leakage. In order to satisfy this, highly accurate measurement and injection control are required.
Therefore, the applicants of this invention have ever developed a molding machine capable of injection-molding metallic goods which are favorably molded, even if the molten metallic material is in the liquid phase state or in the semi-molten state, by carrying out molding with that injection device mounted on a machine base slantwise thereto with the nozzle member side downward, which is comprised of a melt cylinder having a heating means around it, a nozzle member of which the rear inside is formed into a measuring chamber and is attached at the tip of the melt cylinder so as to be freely attachable and detachable, a hollow stirring shaft with stirring blades on the outer peripheral wall in the melt cylinder, and an injection rod which is inserted into the stirring shaft and of which the plunger is inserted into the measuring chamber and which is movably fitted freely forwards and backwards.
In the injection device adopted for this injection molding machine, the measuring chamber is in the nozzle member at the tip and bottom of the melt cylinder mounted slantingly, therefore, when sludge (metallic oxide) produced on the surface of a molten metal (hereafter called a molten metal) is taken into the molten metal in a form of minute particles by being stirred in the melt cylinder, it is prone to precipitate in the periphery of the opening of the measuring chamber at the bottom, and this is absorbed into the measuring chamber together with the molten metal by the backward movement of the plunger.
Even if the minute particles in this sludge pass through the plunger flow passage formed by a gap formed for preventing the material from flowing back and are mixed into a product, they do not have an influence on the appearance and strength of it, however, large particles jams the flow passage and cause failures of measurement and injection-filling, or causes instability of measurement. Therefore, it is necessary to prevent the sludge from exerting the evil influence on forming by some means or other.
This invention has been devised considering the circumstances described above, and the purpose thereof is to provide a new injection device for a low melting point metallic material capable of preventing the sludge from flowing into the measuring chamber, and also stably performing supply of a metallic material and measurement of a molten metal by dividing the inside of the melt cylinder into a melt stirring part and a molten metal flow passage part.
This invention for the above purpose relates to an injection device for a low melting point metallic material, wherein the device is comprised of a melt cylinder having a heating means around it, a nozzle member of which the rear part is formed into a measuring chamber and which is mounted to be freely attachable and detachable at the tip of the melt cylinder, a hollow stirring shaft having stirring blades on the outer periphery of the shaft in the melt cylinder, and an injection rod which is inserted into the stirring shaft so as to be freely movable forwards and backwards and of which the plunger at the tip is inserted into the measuring chamber, and wherein the device is slantingly installed on a machine base with the nozzle member side downwards, and wherein the peripheral end face of the opening of the measuring chamber faced to the inside of the melt cylinder of the above nozzle is projectingly formed into an annular bearing; the above-mentioned stirring shaft is supported to be freely rotatable by the bearing member in the nozzle member and the rear end face of the melt cylinder with suction ports bored in the wall of the shaft tip part; the inside of the melt cylinder is partitioned by the stirring shaft into a melt stirring part provided with a material supply port and a molten metal reservoir communicating with the above-mentioned measuring chamber; and the material supply port is arranged on the upper side part of the melt cylinder which is at a temperature in the range not exceeding the melting point of the low melting point metallic material.
Moreover, the above-mentioned stirring shaft is supported by the above-mentioned nozzle member with the inner diameter of the tip part enlarged; the shaft has lots of minute holes on the peripheral wall between the bearing tip end and the above-mentioned suction ports; the inside of the melt cylinder tip end where the holes are positioned functions as a sludge reservoir by the slant installation; and the shaft has an overflow outflow port bored in the side wall above the molten metal surface.
Further, the plunger at the tip of the above-mentioned injection rod is mounted with a ring valve having seal rings buried in the outer peripheral surface so that the valve is freely movable forwards and backwards on the outer periphery thereof, and the flow passage formed between the ring valve and the plunger is made to be opened or closed according to contact or separation between the rear end face of the ring valve and the seat ring serving also as a guide of the rear part of the plunger, and thereby the plunger is put into the above-mentioned measuring chamber so as to be freely movable.